Fabrication method for adhesive pressure bonding two components together with closed-loop control

ABSTRACT

Two components are bonded together in a bonding apparatus using a bonding medium of malleable metallic spheres and a curable adhesive. The two components are bonded by positioning the components in a facing-but-spaced-apart relation in the bonding apparatus with the spheres and the adhesive between the first component and the second component. The bonding apparatus forces the first component toward the second component with sufficient force to bond the spheres to the first component and to the second component, while monitoring at least one measured bonding reaction of the first component and the second component, and controlling the bonding apparatus responsive to the step of monitoring. The adhesive is thereafter cured, optionally with the bonding pressure released and the assembly removed from the bonding apparatus.

This invention relates to the pressure bonding of two componentstogether with a curable adhesive and malleable metal spheres, and moreparticularly to such bonding where one or both of the components arefragile.

BACKGROUND OF THE INVENTION

In one form of an infrared sensor device, a sensor chip assembly (SCA)is bonded to the mounting platform of a cryostat to form a bondedassembly. The sensor chip assembly is the active sensor component, andthe cryostat is supported on an aiming structure such as a gimbal. Thedetector plane of the sensor chip assembly must be aligned extremelyprecisely with respect to a reference datum plane, to ensure that thesensor chip assembly is pointed in the proper direction by the aimingstructure during service. In some designs, alignments must be achievedbetween the two planes on the order of 10 arcseconds or better.

The sensor chip assembly is a microelectronic device which includes adetector and a readout that are fabricated by microelectronictechniques, and then joined together. The sensor chip assembly is arelatively fragile structure that may be easily damaged by evenrelatively small forces that exceed its load limit. Such damage mayinclude mechanical cracking or breaking, or the damage may be moresubtle in the form of a degradation in electrical performance withoutcracking or breaking. The mounting platform to which the sensor chipassembly is bonded usually is a more-robust mechanical structure.

To accomplish the bonding, the sensor chip assembly and the mountingplatform are carefully aligned in a bonding apparatus. The bondingapparatus is an ultra-high-precision device which is custom adjusted foreach bonded assembly to account for small structural variations thatwould otherwise result in an unacceptable misalignment of the sensorchip assembly and the reference datum plane in the absence of care takento ensure proper alignment. Current practice involves dispensing aquantity of curable adhesive between the sensor chip assembly and themounting platform, and the two components are pressed together andconstrained in place by the bonding apparatus until the adhesive iscured.

The bonding apparatus is used to maintain the correct alignment untilthe adhesive cures sufficiently past the stage at which it may creep anddeform during curing, which may require several hours. The alignmentmust be forcefully maintained because, if the bonded structure wereremoved from the bonding apparatus too early and before curing iscomplete, the slight shape change of the adhesive during curing couldproduce a misalignment between the sensor chip assembly and thereference datum plane that would be unacceptable. The bonding apparatusprovides sufficient constraint during curing of the adhesive andprevents such shape change and misalignment.

While this approach is operable and works well in a laboratory setting,it is uneconomical in a production operation. In production, theprecision bonding apparatus is tied up with each individual assembly foran excessively long time by the need to prevent movement of the sensorchip assembly until the adhesive cures sufficiently, which may beseveral hours. The bonding apparatus is quite expensive, and it istherefore not possible to supply a large number of them consistent withthe production requirement to fabricate a large number of the bondedassemblies. There is therefore a need for an approach that produces therequired alignment of the bonded components in the assembly, but whichis more suitable for a production operation. The present inventionfulfills this need, and further provides related advantages.

SUMMARY OF THE INVENTION

The present invention provides a method for fabricating a structure fromtwo (or more) components. It is particularly useful when one or more ofthe components is relatively fragile, as in the case where one of thecomponents is a microelectronic device such as a sensor chip assembly.Damage to such fragile components is avoided by carefully controllingthe loads applied to the structure during the bonding operation. Thepresent approach is highly reproducible and does not require thejudgments of a skilled technician during the bonding operation.

In accordance with the invention, a fabrication method comprises thesteps of providing a first component and a second component, positioningthe first component in facing-but-spaced apart relation to the secondcomponent, and placing a bonding medium between the first component andthe second component. The bonding medium comprises at least twomalleable spheres made of a metal that bonds to both the first componentand to the second component when subjected to a sufficiently largeforce, and a quantity of an uncured adhesive. The first and secondcomponents may be of any operable types. In a case of interest, thefirst component is a sensor chip assembly. The second component may be amounting platform. A preferred metal for use in the spheres is malleableindium metal.

The method further includes bonding the first component to the secondcomponent using the bonding medium by supplying a bonding apparatushaving at least one force actuator. The bonding apparatus presses thefirst component against the second component in afacing-but-spaced-apart relation, with the bonding medium therebetweenand with a sufficient bonding force to bond the malleable spheres bothto the first component and to the second component. There may be atleast two independently controllable force actuators, or a single forceactuator may be used. Simultaneously with the pressing, at least onemeasured bonding reaction of the first component and the secondcomponent is monitored, and the force actuators of the bonding apparatusare controlled responsive to the step of monitoring. The adhesive isthereafter cured.

In one particularly preferred embodiment, the steps of placing and thebonding apparatus pressing are performed cooperatively by positioningthe first component and the second component in a facing relationship inthe bonding apparatus, dispensing the uncured adhesive between the firstcomponent and the second component, positioning the spheres in theadhesive, bringing the first component, the second component, and thespheres into touching contact with each other, and forcing the firstcomponent toward the second component with sufficient force to bond thespheres to the first component and to the second component.

In the basic process, the step of controlling preferably includes thesteps of providing a set of bonding reaction limitations, comparing themeasured bonding reactions with the respective set of bonding reactionlimitations, and sending control signals to the at least one forceactuator responsive to the step of comparing. The step of providing aset of bonding reaction limitations preferably includes evaluating a setof stresses that cause damage to the first component, and selecting theset of bonding reaction limitations responsive to the step of evaluatingthe set of stresses. The bonding apparatus loading may otherwise beconducted according to a preselected load profile. The step ofcontrolling may also include the step of determining a set of maximumstresses applied to the first component.

In the preferred processing, the step of curing the adhesive includesthe step of removing the bonding force prior to completion of fullcuring of the adhesive. That is, the bonding spheres are placed in theadhesive, and the bonding apparatus is used to force the componentstogether into their final aligned positions. The bonded structure isthereafter removed from the bonding apparatus and set aside to allow theadhesive to cure. The components are held together in the desiredposition and orientation by the adhesion of the malleable spheres to thecomponents until the adhesive fully cures, avoiding the need to keep thecomponents in the bonding apparatus until the adhesive is cured. Thespheres rather than the bonding apparatus provide the necessaryconstraint during the remainder of the curing process. Processthroughput is greatly increased, reducing the manufacturing costs forthe product.

The use of malleable metals and adhesives between electronic componentsis known in other contexts, such as in the bonding of an infrareddetector to a readout integrated circuit in a hybridization or “flipchip” using deformable metallic bumps. However, the malleable metals arenot employed in a bonding operation like that of the present approach,where they constrain the deformation of the adhesive during curing. Thatis, in these other approaches an uncured adhesive is not applied priorto the bonding operation, and the bumps do not serve to constrain theadhesive during the curing of the adhesive.

Other features and advantages of the present invention will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings, whichillustrate, by way of example, the principles of the invention. Thescope of the invention is not, however, limited to this preferredembodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block flow diagram of a fabrication method;

FIG. 2 is a schematic elevational view of a bonding apparatus; and

FIGS. 3-6 are a series of schematic elevational views of the bondingapparatus and components during the bonding operation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts a fabrication method for bonding together two componentsusing a bonding medium. A first component is provided, numeral 20, and asecond component is provided, numeral 22. A bonding medium is provided,numeral 24. The bonding medium comprises at least two, and preferably atleast three, malleable spheres made of a malleable metal that bonds toboth the first component and to the second component when subjected to asufficiently large force, and a quantity of an uncured adhesive.

The first component is bonded to the second component using the bondingmedium, numeral 26. The bonding step 26 includes supplying a bondingapparatus having at least one force actuator, numeral 28, andpositioning the first component and the second component in the bondingapparatus in a facing-but-spaced-apart relation without the bondingmedium present, numeral 30.

FIG. 2 schematically illustrates the bonding apparatus 50 having avacuum chuck 52 that holds one of the two components, here the firstcomponent 54. The second component 56 is supported on a load cell 58,preferably with an upper face 80 of the second component 56 lying in ahorizontal plane. An actuator 60, in this case a stepper motor, movesthe vacuum chuck 52 and thence the first component 54 parallel to aZ-axis 62. There may optionally be multiple actuators that independentlymove different portions of the first component 54 or that move thesecond component 56. A controller 64 receives a Z-position signal 66from the actuator 60 and a load signal 68 from the load cell 58, andsends a motion control command 70 to the actuator 60. The controller 64includes a microprocessor which receives the signals 66 and 68, sendsthe command 70, and performs calculations by which the command 70 isderived from the signals 66 and 68 and other information as discussedbelow.

In the preferred case, the first component 54 is a sensor chip assembly(SCA) of an infrared detector system, and the second component 56 is themounting platform of a cryogenic Dewar to which the sensor chip assembly54 is mounted. The sensor chip assembly typically includes a detectorchip and a readout integrated circuit. One or both of these elements ofthe sensor chip assembly is mechanically and electronically fragile.Even relatively small forces of about 1 kilogram or less applied to thesensor chip assembly may cause it to fracture or, if not fracture, tostress and strain in a manner that causes it to perform in anunsatisfactory manner during subsequent service. The magnitudes of thestresses and strains that cause damage are known for the sensor chipassembly from independent studies of the effects of various types ofstresses and strains on the mechanical integrity and electricalperformance of the sensor chip assembly. The present approach isparticularly advantageous for bonding such fragile components, becauseit monitors the bonding forces and controls the bonding processresponsively so that the forces applied are below the limits that causedamage to the components being bonded.

In this preferred case of the bonding of the sensor chip assembly firstcomponent 54 and the mounting platform second component 56, thecomponents 54 and 56 must be aligned with each other very precisely, sothat the detector plane of the sensor chip assembly is aligned to areference datum plane to within about 10 arcseconds. The vacuum chuck 52is mounted to a support structure (not shown) that facilitates theprecise alignment. The precise alignment must be maintained in the finalbonded structure.

Returning to the discussion of FIG. 1, the bonding medium is positionedon the upper face 80 of the second component 56. The bonding mediumincludes two or more malleable spheres 72 positioned between the firstcomponent 54 and the second component 56. For the present applications,the malleable spheres are preferably metal, most preferably indiummetal. Other malleable metals such as tin, germanium, gold, and the likemay be used instead of indium. As used herein, the term “sphere” is aterm of art referring to a metallic mass that connects twomicroelectronic structures mechanically and in some cases electrically.The use of the term “sphere” does not imply any particular shape andspecifically does not require a spherical shape. The “sphere” mayinitially be of any operable shape, but in the presently preferredapproach the sphere 72 is initially a roughly spherical mass of themetal that is deformed and flattened during the subsequent bonding. Thebonding medium further includes an adhesive layer 74 that is alsopresent between the first component 54 and the second component 56. Anyoperable adhesive may be used, but a preferred adhesive is anepoxy-based adhesive. To apply the bonding medium, a quantity of theadhesive layer 74 is dispensed onto the upper face 80, and then thespheres 72 are dropped into the adhesive, numeral 32. FIG. 3 illustratesthe elements at this stage.

The first component 54 and the spheres 72 are thereafter brought intotouching contact with each other, and the second component 56 and thespheres 72 are brought into touching contact with each other, numeral34. (Equivalently, the spheres could be positioned between the firstcomponent and the second component in light but unbonded contact to eachone, and the uncured adhesive dispensed into the remaining space betweenthe first component and the second component. This alternative is notpreferred, because typically the viscosity of the uncured adhesive istoo high to flow easily into the space between the first component andthe second component.) Because the spheres 72 are already resting on theupper face 80 of the second component 56 after step 32, this touchingcontact is accomplished by lowering the first component 54 (held in thevacuum chuck 52) using the actuator 60 until it just touches the spheres72 and gently forcing them into full contact with the upper face 80.

The bonding apparatus forces the first component 54 toward the secondcomponent 56 with a sufficient bonding force to bond the spheres 72 tothe first component 54 and to the second component 56, numeral 36. Inthe preferred case, the facing surface of the sensor chip assembly firstcomponent 54 is silicon, and the facing surface of the mounting platformsecond component 56 is a ceramic. The spheres are preferably indium,which deforms and flattens under the applied bonding force and, uponreaching a sufficiently high bonding pressure of about 50 grams, coldwelds to the first component 54 and to the second component 56. FIG. 4illustrates the elements at this stage.

During this step 36 and simultaneously therewith, the controller 64monitors at least one measured bonding reaction of the first component54 and the second component 56 as measured by the load cell 58, as theload signal 68, numeral 38. The bonding reaction may be an axial load,such as the Z-axis force F_(z) measured by the load cell 58 and appliedparallel to the Z-axis 62. Transverse forces perpendicular to the axis62 and torques may be measured as well and provided to the controller64.

The controller 64 controls the bonding apparatus 50 responsive to thestep of monitoring 38, numeral 40. The steps of forcing 36, monitoring38, and controlling 40 are performed simultaneously. The step ofcontrolling 40 preferably includes providing a set of bonding reactionlimitations for the components 54 and/or 56, such as the stress andstrain limitations discussed earlier. Such limitations are determinedseparately by performing studies of the magnitudes of stresses andstrains that cannot be exceeded without damaging the components, in thiscase the sensor chip assembly first component 54. The measured bondingreactions of step 38 are compared with the respective set of bondingreaction limitations, and control signals are sent to the actuator 60responsive to the step of comparing. Thus, for example, it may bedetermined that the axial force F_(z) applied parallel to the Z-axis 62may not exceed a value F_(z,max) (the bonding reaction limitation forthis case) without causing damage to the sensor chip assembly. Theactuator 60 is controlled so as not to exceed this value of axial force.In other cases, the actual loading situation may be more complex, andcombinations of internal stresses and strains within the components maybe taken into account in determining how much axial force may be appliedby the actuator 60, and the actuator control command 70 is selectedresponsively. For example, strain gauges may be applied to the firstcomponent 54, and their outputs provided to the controller 64. Thecontroller 64 makes the calculations of internal stresses and strainsfrom the applied forces by conventional mechanical analysis techniquessuch as stress-strain data and a regression curve obtained by fitting acurve to the data.

The bonding apparatus actuator loading of step 36 may be conductedinitially according to a preselected load profile as a function of time.However, the application of the load according to this load profile istypically modified responsive to the steps 38 and 40. That is, if thepreselected load profile is producing too high a loading in the fragilecomponent(s), then the rate of load application may be slowed or haltedto permit the indium to flow to lessen the rate of increase of thestresses and strains in the component(s).

During the steps 36, 38, and 40, the adhesive 74 begins to cure. Fullcuring takes a good deal of time beyond the extent of these steps 36,38, and 40, however. Therefore optionally but preferably, the bondingforce and constraint applied by the actuator 60 are removed prior tocompletion of full curing of the adhesive 74, numeral 42, as seen inFIG. 5. The assembly of components 54 and 56 with the bonding medium ofspheres 72 and adhesive 74 is removed from the bonding apparatus 50 andset aside to allow the adhesive to fully cure, numeral 44 and FIG. 6. Inthe prior approach, curing was accomplished with the assembly remainingin the bonding apparatus 50, but this ties up the expensive bondingapparatus for an extended period of time, typically about 24 hours withadhesives of interest, and is impractical for production operations.

The spheres 72 which are adhered to the components 54 and 56 hold thecomponents 54 and 56 in exactly the correct orientation and separationwhile the adhesive 74 is curing in step 44. If the spheres were notpresent to serve as the constraint against deformation, the adhesive 74would deform slightly as it cures. The experience of the inventors hasshown that even this slight deformation is sufficient to result in anunacceptably large misalignment of the sensor chip assembly firstcomponent 54 with the reference datum plane. The use of the spheres 72therefore holds the components 54 and 56 in the correct orientation andposition during the curing of the adhesive 74, while permitting thecuring assembly to be removed from the bonding apparatus 50 for reasonsof process economics.

The feedback control of bonding force applied by the actuator 60practiced during steps 36, 38, and 40 is necessary in order to use thisbonding approach utilizing a bonding medium of spheres 72 and adhesive74. The presence of the spheres 72 and their resulting concentratedforce loading on the components can produce damage in the sensor chipassembly first component 54 unless great care is taken during forceapplication by the actuator 60 not to exceed the bonding reactionlimitations and the maximum permissible stresses and strains within thecomponent(s). The feedback control of steps 36, 38, and 40 provides thiscareful force application.

The present invention was reduced to practice using the bondingapparatus 50 like that of FIG. 2, and the fabrication approach of FIG.1. Five assemblies of sensor chip assembly first component 54 andmounting platform second component 56 were prepared using thisapparatus. The controller 64 was programmed so that F_(z,max) wasestablished at 120 grams (the bonding reaction limitation in this case)for the geometry used. The four bonding spheres 72 were initially indiumspheres of diameter 0.010 inch, and the final desired result was aspacing between the first component 54 and the second component 56 of0.005 inch (that is, with the height of the spheres reduced to halftheir initial diameter). During the sphere-bonding operation of steps36, 38, and 40, the actuator 60 was moved at a constant rate until F_(z)exceeded 120 grams, at which time the movement was halted, and thespheres 72 were allowed to flow under the applied force until F_(z) fellto a relief force of below 120 grams, in this case 105 grams. Thecompressive motion of the actuator 60 was then resumed. This loading andrelieving cycle was automatically repeated several times until the finalthickness of 0.005 inch was reached. Step 42 was included in thisprocessing, so that the assemblies were removed prior to completecuring, after a pressing time in the bonding apparatus of about 1minute, and set aside to complete the curing for a total curing time ofabout 24 hours. The bonding apparatus was therefore immediatelyavailable to bond other assemblies in a production operation.

As a result of the feedback control of the actuator 60, no damage wasproduced in the sensor chip assembly first component 54, as determinedby visual inspection for cracking and electrical tests of operability.The sensor chip assembly first component 54 and the mounting platformsecond component 56 were aligned within 10 arcseconds in the finalarticle with cured adhesive.

Comparative testing was performed. In one type of comparative test, thebonding operation was repeated without the use of the spheres and withonly adhesive bonding the components together. After removal of thepartially bonded components from the bonding apparatus, there was apost-alignment creep deformation of the adhesive during curing thatresulted in misalignments of tens of arc minutes, which is unacceptablefor the sensor application of interest. This test demonstrated that,absent the use of the spheres, the components must remain in the bondingapparatus to constrain such post-alignment creep deformation for up toabout 24 hours, preventing the use of the bonding apparatus in bondingother components for that period. The use of the spheres is thereforenecessary to facilitate the production bonding operation.

In a second type of comparative test, twelve assemblies of sensor chipassembly and mounting platform were prepared using a human-controlledapparatus which was otherwise like the apparatus of FIG. 2. The bondingmedium included the spheres and the adhesive. The testing demonstratedthat even a skilled human operator did not react sufficiently quickly toavoid damage to the sensor chip assemblies as the load varied at aboutthe bonding load. Every one of the twelve manually produced assembliescracked or otherwise suffered damage by the inability of the humanoperator to compensate for stress or strain buildups in the fragilesensor chip assembly first component 54. That is, the cooperative use ofthe spheres 72 and adhesive 74, which are necessary for an acceptableproduction rate, also requires the use of the computerfeedback-controlled bonding apparatus 50.

Although a particular embodiment of the invention has been described indetail for purposes of illustration, various modifications andenhancements may be made without departing from the spirit and scope ofthe invention. Accordingly, the invention is not to be limited except asby the appended claims.

What is claimed is:
 1. A fabrication method comprising the steps ofproviding a first component and a second component; positioning thefirst component in facing-but-spaced apart relation to the secondcomponent; placing a bonding medium between the first component and thesecond component, the bonding medium comprising at least two malleablespheres made of a metal that bonds to both the first component and tothe second component when subjected to a sufficiently large force, and aquantity of an uncured adhesive; thereafter bonding the first componentto the second component using the bonding medium, the step of bondingincluding the steps of supplying a bonding apparatus having at least oneforce actuator; the bonding apparatus pressing the first componentagainst the second component in a facing-but-spaced-apart relation, withthe bonding medium therebetween, with a sufficient bonding force to bondthe malleable spheres both to the first component and to the secondcomponent, simultaneously monitoring at least one measured bondingreaction of the first component and the second component, andsimultaneously controlling the bonding apparatus responsive to the stepof monitoring, and thereafter curing the adhesive.
 2. The method ofclaim 1, wherein the step of controlling includes the steps of providinga set of bonding reaction limitations, comparing the at least onemeasured bonding reaction with the respective set of bonding reactionlimitations, and sending control signals to the at least one forceactuator responsive to the step of comparing.
 3. The method of claim 2,wherein the step of providing a set of bonding reaction limitationsincludes the steps of evaluating a set of stresses that cause damage tothe first component, and selecting the set of bonding reactionlimitations responsive to the step of evaluating the set of stresses. 4.The method of claim 1, wherein the steps of placing and the bondingapparatus pressing include the steps of positioning the first componentand the second component in a facing relationship in the bondingapparatus, dispensing the adhesive between the first component and thesecond component, positioning the spheres in the adhesive, bringing thefirst component and the spheres, and the second component and thespheres, into touching contact with each other, and forcing the firstcomponent toward the second component with sufficient force to bond thespheres to the first component and to the second component.
 5. Themethod of claim 1, wherein the step of controlling includes the step ofdetermining a set of maximum stresses applied to the first component. 6.The method of claim 1, wherein the step of providing a first componentand a second component includes the steps of providing a sensor chipassembly as the first component.
 7. The method of claim 1, wherein thestep of providing a first component and a second component includes thesteps of providing a sensor chip assembly as the first component, andproviding a mounting platform as the second component.
 8. The method ofclaim 1, wherein the step of the bonding apparatus pressing includes thestep of the bonding apparatus loading according to a preselected loadprofile.
 9. The method of claim 1, wherein the step of placing a bondingmedium includes the step of furnishing spheres comprising a metalselected from the group consisting of indium, tin, germanium, and gold.10. The method of claim 1, wherein the step of curing the adhesiveincludes the step of removing the bonding force prior to completion offull curing of the adhesive.
 11. A fabrication method comprising thesteps of providing a first component and a second component; providing abonding medium comprising at least two malleable spheres made of a metalthat bonds to both the first component and to the second component whensubjected to a sufficiently large force, and a quantity of an uncuredadhesive; bonding the first component to the second component using thebonding medium, the step of bonding including the steps of supplying abonding apparatus having at least one force actuator, positioning thefirst component and the second component in a facing relationship toeach other in the bonding apparatus, dispensing the adhesive between thefirst component and the second component, positioning the spheres in theadhesive, thereafter bringing the fist component, the second component,and the spheres into touching contact with each other, the bondingapparatus forcing the first component toward the second component withsufficient force to bond the spheres to the first component and to thesecond component to form an assembly, monitoring at least one measuredbonding reaction of the first component and the second component,controlling the bonding apparatus responsive to the step of monitoring,the steps of forcing, monitoring, and controlling being performedsimultaneously, and thereafter curing the adhesive.
 12. The method ofclaim 11, wherein the step of controlling includes the step of providinga set of bonding reaction limitations, comparing the measured bondingreactions with the respective set of bonding reaction limitations, andsending control signals to the at least one force actuator responsive tothe step of comparing.
 13. The method of claim 12, wherein the step ofproviding a set of bonding reaction limitations includes a step ofevaluating a set of stresses that cause damage to the first component,and selecting the set of bonding reaction limitations responsive to thestep of evaluating the set of stresses.
 14. The method of claim 11,wherein the step of controlling includes the step of determining a setof maximum stresses applied to the first component.
 15. The method ofclaim 11, wherein the step of providing a first component and a secondcomponent includes the steps of providing a sensor chip assembly as thefirst component.
 16. The method of claim 11, wherein the step ofproviding a first component and a second component includes the steps ofproviding a sensor chip assembly as the first component, and providing amounting platform as the second component.
 17. The method of claim 11,wherein the step of the bonding apparatus pressing includes the step ofthe bonding apparatus loading according to a preselected load profile.18. The method of claim 11, wherein the step of placing a bonding mediumincludes the steps of furnishing spheres comprising a metal selectedfrom the group consisting of indium, tin, germanium, and gold.
 19. Themethod of claim 11, wherein the step of curing the adhesive includes thestep of removing the bonding force prior to completion of full curing ofthe adhesive, and removing the assembly from the bonding apparatus. 20.A fabrication method comprising the steps of providing a sensor chipassembly and a mounting platform; positioning the sensor chip assemblyin facing-but-spaced apart relation to the mounting platform; placing abonding medium between the sensor chip assembly and the mountingplatform, the bonding medium comprising at least two malleable spheresmade of a metal selected from the consisting of indium, tin, germanium,and gold, and a quantity of an uncured adhesive; bonding the sensor chipassembly to the mounting platform using the bonding medium, the step ofbonding including the steps of supplying a bonding apparatus having aforce actuator; the bonding apparatus pressing the sensor chip assemblyagainst the mounting platform, with the bonding medium therebetween,with a sufficient bonding force to bond the malleable spheres both tothe sensor chip assembly and to the mounting platform to form anassembly, simultaneously monitoring at least one measured bondingreaction of the sensor chip assembly and the mounting platform, andsimultaneously controlling the bonding apparatus responsive to the stepof monitoring, and thereafter curing the adhesive, the step of curingthe adhesive including the steps of removing the bonding force prior tocompletion of full curing of the adhesive, and removing the assemblyfrom the bonding apparatus prior to full curing of the adhesive.